BIOL 2015 – Evolution and...
11
1 BIOL 2015 – Evolution and Diversity Lab 6: Fungi Introduction The Kingdom Fungi consists of the Divisions Chytridiomycota, Zygomycota, Ascomycota, and Basidiomycota. The latter three groups are primarily terrestrial. As decomposers, with rapid growth and high surface-to-volume ratio, fungi have an intimate contact with their environment that is very different from most other organisms. An extensive mycelium can bind soil particles and litter and penetrate most of the upper soil volume. Maintenance of this intimate fungal environment requires that all parts of the fungus be metabolically active. The Chytridiomycota we typically order is occasionally unavailable so we may not have the opportunity examine this group. Fungal associations: Lichens and Mycorrhizae All fungi are heterotrophic and most are saprotrophic, but the higher fungi display a diversity of other relationships. Several species of Ascomycetes and several Basidiomycetes combine with green algae or even cyanobacteria to form lichens. Lichens are extremely widespread in nature and can tolerate severe environments. They are even found close to the South Pole, one of the drier, colder sites in the world. They are also abundant in deserts and alpine areas. For example, Cladonia rangiferina, a light-colored fruticose lichen belonging to the Cladoniaceae family, is an extremely important food for caribou and other large grazers in the arctic. Despite being tolerant of severe environments, lichens are very sensitive to air pollution. Lichens have almost disappeared from the Los Angeles basin and there is evidence that the level of pollution has crossed the injury threshold of the native lichens in the San Bernardino Mountains and the southern aspect of the Sierra Nevada range. Certain fungi play a crucial role in ability of higher plants to acquire mineral nutrients. These fungi form associations with plant roots called mycorrhizae. The fungus obtains carbohydrates from the plant while the plant benefits because the fungus essentially enlarges their root system, thereby allowing them to access to the mineral nutrients from a larger area.
Transcript of BIOL 2015 – Evolution and...
1
BIOL2015–EvolutionandDiversityLab6:Fungi
Introduction
TheKingdomFungiconsistsoftheDivisionsChytridiomycota,Zygomycota,Ascomycota,andBasidiomycota.Thelatterthreegroupsareprimarilyterrestrial.Asdecomposers,withrapidgrowthandhighsurface-to-volumeratio,fungihaveanintimatecontactwiththeirenvironmentthatisverydifferentfrommostotherorganisms.Anextensivemyceliumcanbindsoilparticlesandlitterandpenetratemostoftheuppersoilvolume.Maintenanceofthisintimatefungalenvironmentrequiresthatallpartsofthefungusbemetabolicallyactive.TheChytridiomycotawetypicallyorderisoccasionallyunavailablesowemaynothavetheopportunityexaminethisgroup.
Fungalassociations:LichensandMycorrhizae
Allfungiareheterotrophicandmostaresaprotrophic,butthehigherfungidisplayadiversityofotherrelationships.SeveralspeciesofAscomycetesandseveralBasidiomycetescombinewithgreenalgaeorevencyanobacteriatoformlichens.Lichensareextremelywidespreadinnatureandcantoleratesevereenvironments.TheyareevenfoundclosetotheSouthPole,oneofthedrier,coldersitesintheworld.Theyarealsoabundantindesertsandalpineareas.Forexample,Cladoniarangiferina,alight-coloredfruticoselichenbelongingtotheCladoniaceaefamily,isanextremelyimportantfoodforcaribouandotherlargegrazersinthearctic.Despitebeingtolerantofsevereenvironments,lichensareverysensitivetoairpollution.LichenshavealmostdisappearedfromtheLosAngelesbasinandthereisevidencethatthelevelofpollutionhascrossedtheinjurythresholdofthenativelichensintheSanBernardinoMountainsandthesouthernaspectoftheSierraNevadarange.
Certainfungiplayacrucialroleinabilityofhigherplantstoacquiremineralnutrients.Thesefungiformassociationswithplantrootscalledmycorrhizae.Thefungusobtainscarbohydratesfromtheplantwhiletheplantbenefitsbecausethefungusessentiallyenlargestheirrootsystem,therebyallowingthemtoaccesstothemineralnutrientsfromalargerarea.
2
Evolutionaryrelationshipsanddistinguishingcharacters
Thehigherfungiappeartoberelatedtooneanother.Eachhascellwallsmadeofchitin.Themostprimitiveofthethreedivisions,Zygomycota,iscoenocytic(multinucleatecellwhichcanresultfrommultiplenucleardivisions).InAscomycota,porousseptations(cellwalls)occur,buttheporesarelargeenoughthatnucleicanactuallypassthrough.Theseptationsofthebasidiomyceteshaveporesgenerallytoosmallforthistooccur.Allthreegroupshavenoflagellatedorciliatedstagesandcontainnocentrioles.Additionally,themitoticspindleformsinsidethenuclearmembrane,whichdoesnotbreakdownduringnucleardivision
SexualReproduction
Sexualreproductionusuallyinvolvesthefusionoftwodistincthyphae.Inthetwomoreadvanceddivisionsthetwonucleidonotfuseimmediately;rather,afilamentwithmorethanonenucleuspercellfromdifferentindividualsisformed.Thisisheterokaryosis.Truediploidyoccurswhenthenucleifuse.Meiosisusuallyoccursimmediatelyafterwardsresultingintheformationofhaploidspores.Theresultinghaploidsporesgerminatetoformnewmycelia.Membersofallthreegroupsoftenproducespecialstructurestoaidsporedispersal.Forexample,amushroomisanexampleofa"fruiting"body(composedofmanyheterokaryoticcells)fromwhichsporesdisperseinsomebasidiomycetes.
Examples
Someimportantorfamiliargenerainclude:Rhizopus,thecommonbreadmold,aZygomycete;Clavicepspurpurea,ergot,aplantparasitethatcausessevereillnessordeathinhumans,anascomycete;Penicillium,anascomycetegenuswithinwhichsomefermentingspeciesformcheeses,whileothersarethesourceoftheantibioticpenicillin.Yeasts(Saccharomyces)areunicellularascomyceteswhichfermentsugarsintheproductionofalcoholicbeersandwines,aswellasbread;trufflesandmorels,reproductivestructuresofvariousascomycetespecies,areprizedasgourmetfoods.Amanitaisafamiliarbasidiomycetethatkillsamateurmushroomcollectorseachyearafterthecollectorseatthefruitingbody,unawarethatitishighlytoxic.
Duringthislabfocusontheappearanceandstructureofthehyphae,asthisisthebasicformoftheorganism.Examinecarefullythereproductivestructures.Becausefungiareusuallyfilamentousandgrowinsoil,wood,anddetritusmaterials,muchofourfamiliaritywiththemislimitedtotheirreproductivestructures.
Zygomycota
Rhizopus
Thisfungusisdistributedthroughouttheworld.Onespeciesisusedtofermentriceintosake.Anotherspeciesisusedtoinoculatesoybeanstomaketempeh.Thegenusisusuallysaprophyticbutfrequentlyattacksfruitsandvegetablesthathavebeeninjured.Itoccupiesnon-aquatichabitatsandneverproducesmotilespores.Sexualreproductionisbyconjugation.
3
(A)Examinationofpreparedslide
Findapreparedslidelabeled“Rhizopusconjugation”.Whenyouobservethepreparedslide,trytoobservethedifferentstagesinthedevelopmentofzygosporangia–especiallythestagewherethegametangiahaveformed.
(B)Cultureexamination
(1)ExamineacultureofRhizopus.Notetheappearanceofthecolony.Whatcolorarethehyphae?Whatotherstructurescanyousee?
(2)Examinetheculturewithadissectingmicroscope.Isthemyceliumbranched?Arecrosswallspresent?Notethecharacteristicformationofrhizoids,thesmallroot-likebranchesalongthehyphaegrowingonthesubstrate.
(3)Focusonthedarkcoloredstructures.Thesearesporangia.Thedarkonescontainmassesofmaturesporangiospores(Figure1).Thewhitishonesarenotyetmature.Thesporangialwallisveryfragileandisfrequentlyrupturedwhenpreparingslides.Thebranchsupportingthesporangiumiscalledasporangiophore.
(C)WetMount
Prepareawetmountofsomeofthemyceliumwithsporangiaandexaminewithacompoundmicroscope.Notethecoenocyticmycelium.Locateasporangiophoreandsporangium.Whatcolorarethespores?Isthesporewallsmoothorroughened?
(D)SexualReproduction
(1)Todemonstratesexualreproduction,2differentstrainsofRhizopushavebeengrowntogether.Examineaplatewithadissectingmicroscope.Findanearlystageofconjugationinwhichshort,lateralbranchesarisefromseparatehyphaeandcomeintocontact.Thebranchestypicallybecomeenlargedandhavearelativelydensemassofcytoplasm.Theyaretheprogametangia.
(2)Nextfindstagesinwhichacrosswallhasdividedtheprogametangiaintoaterminalportion,thegametangium(Figure2a,leftpanel,toparrow)andasupportingcellcalledsuspensor.
Figure2a
Figure1
4
(3)Thewallseparatingtheplus(+)andminus(-)gametangiadissolves,thecytoplasmmixes,andnucleipair.Nuclearfusionoccursandthecellformedbytheformergametangiadevelopsathick,darkcolored,roughwall.Thisisthezygospore(Figure2a,leftpanel,middlearrow).Itcanremaindormant,buteventuallymeiosisoccurs.Asporangiumarisesfromthezygospore,afterwhichthehaploidsporesdisperse.
Pilobolus
Thisfungusiscommonlyfoundinpasturesgrowingondung(Figure2b).Thesporangiophoresarephototrophicandcanshootthesporangiaupto2-3metersinthedirectionofabrightlightsource.
(1)ExaminethelivingculturesofPiloboluscrystallinus.Whatistheadaptivesignificanceofhavingphototrophicsporangiophores?
Figure2b
5
6
Ascomycota
Saccharomyces-yeast
Yeastsconsistofasingle,non-motilecell.Theseorganismsreproduceasexuallybybuddinginwhichdaughtercellsareformedatoneorbothendsoftheparentcell.Insexualreproductiontheentirecellbecomesanascuswitheitherfouroreightascospores.Manyoftheyeastssuchasthisoneareofconsiderableeconomicimportancetohumans–theyproducecarbondioxidetoLevinbreadunderaerobicconditionsoralcoholunderanaerobicconditions.
Prepareaslidefromoneofthefermentingculturesandexamineunderhighpoweroroilimmersion.
(1)Notetheshapeandsizeofthecells.Makesureyouwillbeabletodistinguishthemfromothercells.
(2)Lookforbuddingcells.Thesmallcellcontinuestoincreaseinsizeuntilitreachesthesizeoftheparentandeventuallybreaksfree.Beforebecomingfree,however,itmighthavebeguntobud;thusitisn'tuncommontoseechainsof2-4cellsinvariousstagesofbudding.
PenicilliumandAspergillus
Thesetwokindsoffungiareextremelycommonandare,infact,laboratory"weeds".Althoughtheyareascomycetes,onlyasexualstageswillbeexamined.
Findapreparedslidelabeled"MoldTypes"or"Penicillium,Aspergillus,Rhizopus"
(1)Examinethedemonstrationculturessetupforyou.Isthemyceliumseptate?Asexualreproductionoccurswiththeformationofconidiosporesatthetipsofanerectbranchcalledtheconidiophore(Figure3).Aretheythesameinbothgenera?Insomeascomycetes,thetipoftheconidiophorehasanenlargedcellcalledthevesicle,towhichareattachedshortbranchescalledsterigmata(Figure3,arrow).Theconidiosporescanbefoundattachedtotheendsofthesterigmata.Inothersthesterigmatamaybebranchedaswell.
(2)WhatistherelationshipbetweenPenicilliumandpenicillin?
Eurotiumchevalieri
Findalivingculture.Youwillseesmall,roundstructuresyellowincolorunderadissectingmicroscope.Thesearethecleistothecia-ascocarpsthatcompletelyenclosethematureasciandreleasetheascocporeswhentheyruptureordegrade.Youmayalsoseesmallfuzzystructures(conidiaandconidiophoreslikethoseinAspergillus).
Figure3
7
8
Basidiomycota
Thesefungiareregardedasamongthemoreadvancedbasidiomycetesbecauseofthebasidiumandthefleshyfruitingbody.
(1)Findthefollowingonafreshmushroom:pileus(cap);stipe(stalk);lamellae(gills);annulus(collar);volva(cup).Whatistheoriginoftheannulusandvolva?(answer:remnantofthepartialveil-Asheetoftissueunderamushroomcap.Itstretchesfromthecapmargintothestem,andprotectsthesporebearingtissuesuntilthesporesaremature).Besureyoucanfindthemonallthefreshmushrooms,includingAgaricusbisporus,commonbuttonmushroom.
Cutoneofthesemushroomsinhalf,vertically,andleaveonehalfforsomeoneelsetouse.Carefullyremoveoneofthegillsandmountonaslideinadropofwater,pressingdownonthecoversliptokeepitflat.Findtheterminalbranch-likestructures(sterigmata),towhichareattachedthebasidiospores.Howmanybasidiosporesareineachbasidium?Notedifferencesinsporecoloramongdifferentspecies.
Figure4
9
10
Lichens
Lichensareformedbyasymbioticassociationofafungusandanalga.Thefungusinmostlichenspeciesisanascomycota,butinsomelichensitisabasidiomycota.ThealgaisoneofseveraldistinctspeciesofChlorophytaorCyanobacteria.Thealgafromthisassociationcanusuallysurviveasafree-livingorganism,butthefunguscannot.Thealgaprovidesfoodforthefungus,andthefungusfurnishesmoisture,shelter,andmineralsforthealga.
Vegetativestructure
Examinespeciesoflichensthatdemonstratethethreegeneraltypesoflichengrowthforms:crustose,aflattened,crust-likeform;foliose,amoreorlessleaf-likeappearance;andfruticose,orabranching,shrub-likeform.
Reproductivestructures-Sexualreproductionofthefungalpartner
Onthespecimensavailable,notewhetherthereareanyfruitingbodiesassociatedwiththem.Theseareoftenbrightlycolored.Becausemostlichensareascomycetes,thesefruitingbodiesarelikelytobeascocarps,reproductivestructurescontaininglargenumbersofasciarrangedonapothecia(thecups).Apreparedslideisavailabletoshowyouathinsectionofthisarea.
Asexualreproductionofthelichen
Carefullyexaminethesurfaceofthelichensforsorediaorisidia.Surveythesurfaceofthelichenuntilyoufindanareawhichseemstobecoveredwithalightdustonitandisassociatedwithcracksoropeningsthroughtheupperlichencortex.Examinetheseareascarefullyandyoushouldbeabletoobservesoredia,whicharespecializedfragmentsofthelichencontainingafewalgalcellsandsurroundedbyhyphae.Otherlichensdisplayisidia,whicharetinybranchesonthesurfaceofthelichen.Thesebranchesareactuallyimmaturethalli,alreadywithanupperandlowercortexandcontainingalgalcells.Bythese
Figure5:crustose(left),foliose(middle),andfruticose(right)morphsoflichen
Figure6
11
means,lichensareabletopropagateandactuallymaintainbothmembersofthesymbiosis.Canyouthinkofawaybothmemberscansexuallyreproduceanddispersetheirprogenywhilecontinuingtomaintainasymbioticrelationship?
Mycorrhizae
Certainsoilfungiformassociationswithrootsofvascularplants.Theassociationappearstobenefitbothmembersbecausestudieswithradioactivetracershaveshownthatthefungusreceivescarbohydratesfromthegreenplantwhiletherootsobtainmineralnutrientsthatthefungushasabsorbedfromthesoil.Thesemycorrhizalassociationsarewidespreadthroughoutthevascularplantkingdomandsofarhavebeenfoundinover80%ofthefloweringplantsexamined.
(A)EctomycorrhizaeandEndomycorrhizae
Thetwocommontypesofmycorrhizaeareectomycorrhizaeandendomycorrhizae.Ectomycorrhizaearecharacteristicofcertaintemperatetreessuchasoaks,willows,andconifers.Theyformasheathsurroundingtheroottipswithhyphaepenetratingbetweenthecellsoftherootcortex.Roottipswithectomycorrhizaetakeonacharacteristicappearance,shorterandstubbierthanuninfectedrootsandoftenforming"Y"branches.Ectomycorrhizalfungiareusuallybasidiomycetes,oroccasionallyascomycetes.
Findapreparedslidelabeled"EctotrophicMycorrhiza"andnotethecharacteristicbranchingpattern.
Endomycorrhizaearecommonlyfoundonherbaceousplants,manytropicalandsometemperatetrees.Themyceliumpenetratesthecellsoftheplantrootcortexinthisassociationandformslargevesiclesorbranchingsystemswithinthecells.Endomycorrhizalfungiarezygomycetes.Besureyoucandistinguishecto-versusendomycorrhizae.
Findapreparedslidelabeled"EndotrophicMycorrhiza"andmakesureyoucandistinguishthefungalhyphaeamongthecorticalcellsoftheroot.
![LAB06 - Subprogramas [12-2011]v2](https://static.fdocuments.net/doc/165x107/577ce5031a28abf1038f9e7f/lab06-subprogramas-12-2011v2.jpg)
